1. Field of the Invention
The present invention relates to a fuel storage tank, and more particularly, to a fuel storage tank having separate compartments for fuel and a reducing agent.
2. Description of Related Art
Using a reducing agent in an exhaust gas purification system is well known to those skilled in the art. A typical such system is discussed in a Siemens Aktiengesellschaft pamphlet entitled "SiNOx Nitrogen Oxide Reduction for Stationary Diesel Engines," Order No. A96001-U91-A232, Siemens A G, Bereich Energieerzeugung (KWU), Freyeslebenstra.beta.e 1, 91058 Erlangen, Germany (1994). This system is based on the SCR (Selective Catalytic Reduction) method, which makes use of the fact that nitrogen oxides are converted into nitrogen and water in the presence of urea and suitable catalysts. For this purpose, the diesel engine exhaust gases are passed through an SCR catalytic device which is integrated into the engine exhaust line and into which the reducing agent is introduced in a precisely metered manner.
In a vehicle exhaust gas purification system, it is necessary to provide a tank for the reducing agent. Typically, the reducing agent is stored in a separate storage container or tank spaced from the primary vehicle fuel tanks. A solid reducing agent, such as urea, is dissolved in a liquid, for example, water, for various reasons, among them to facilitate its introduction in precisely metered amounts. Such aqueous solutions of reducing agents crystalize and solidify at relatively high temperatures. For example, a 32.5% urea/water solution solidifies at -11.degree. C. (about 14.degree. F.). If the reducing agent solution freezes, it cannot be pumped from the storage tank and used to purify the engine exhaust.
The need to provide for storage of the reducing agent presents particular problems in a vehicle. First, a separate space must be made available in the vehicle. Then, a separate tank must be provided and brackets and other suitable mounting structure must be provided on the tank and in the vehicle to secure the tank within the space. Using vehicle space to accommodate the reducing agent storage tank reduces the amount of space available for other purposes, notably vehicle payload, and requires moving other vehicle components. Accordingly, a great deal of effort must be devoted to designing a storage tank that uses vehicle space as efficiently as possible and that simplifies mounting the storage tank.